Bacterial respiratory tract infections can plague even the most healthy of individuals. Luckily for these healthy individuals, most of the bacterial respiratory tract infections they contract can be successfully treated with conventional antibiotics. There are some pathogens, however, which have proven very difficult to treat in both healthy and sick individuals. In addition to being difficult to treat, many of these pathogens are opportunistic and tend to infect those whose immune systems are already compromised. Three of these opportunist pathogens are Pseudomonas aeruginosa (P. aeruginosa), Burkholderia cepacia (B. cepacia), and Staphylocoocus aureus (S. aureus) (both wild type and methicillin-resistant).
Susceptibility to bacterial respiratory tract infections is especially high for those individuals who are already plagued by a pulmonary disease such as, for example, cancer, black lung, pneumonia (ex. ventilator-associated), bronchiectasis, cystic fibrosis (CF), and chronic obstructive pulmonary disease (COPD). COPD is a collective term that describes ailments associated with airway obstruction. These ailments include, for example, chronic bronchitis, asthma, and emphysema. COPD is the fourth leading cause of death in the U.S. (120,000 deaths in 2002 alone) and is often linked to smoking. P. aeruginosa, B. cepacia, and S. aureus are prevalent in those individuals with COPD and/or CF.
CF is one of the most common fatal genetic disorders in the United States. CF is most prevalent in the Caucasian population and occurs on an average of one in every 3,300 live births. A mutation in a gene that encodes a chloride channel, the cystic fibrosis transmembrane conductance regulator (CFTR), produces partially functional or completely dysfunctional channels. Depending on the mutation and whether the person carries one or two copies of the mutated allele, the prognosis varies widely: heterozygous individuals are asymptomatic for life while those who are homozygous for the mutation have CF. If patients have the most common CF allele, DF508, they typically die by the age of 36.8.
CF patients develop thick mucus secretions resulting from the disruption of the salt/water balance. These mucus secretions clog bronchial tubes in the lungs and plug exit passages of the pancreas and intestines that often lead to a loss of function of these organs. It is in this thick airway mucus, depleted of oxygen by the metabolic activity of aerobic bacteria, neutrophils, and even epithelial cells, where many opportunistic and pathogenic bacteria thrive.
In CF patients, P. aeruginosa is one of the most common bacteria trapped in the thickened, dehydrated, hypoxic mucus lining in airway epithelia. Chronic lung infection of CF patients by P. aeruginosa is the leading cause of morbidity and mortality associated with the disease. Moreover, while P. aeruginosa infections are typically treatable with antibiotics, this bacterium often converts to a mucoid form that is antibiotic-resistant and incapable of reverting to their nonmucoid antibiotic susceptible counterparts. This is particularly true in CF individuals. As P. aeruginosa, B. cepacia, S. aureus, and other pathogens are continuing to cause bacterial respiratory tract infections in both healthy and immunocompromised individuals, a need exists for additional methods of treating these infections.